The present invention relates to the production of a pipeline gas from a hydrocarbonaceous fuel, and more particularly, to a process for producing a pipeline gas from a product gas produced via the low pressure gasification of coal.
The prior art processes for producing a synthetic pipeline gas from coal are many and varied. U.S. Pat. Nos. 3,854,859, 3,922,148 and 4,208,191 exemplify the typical prior art manufacture of synthetic pipeline gas from coal. In such processes, the coal is typically gasified under relatively high pressure with oxygen or oxygen and steam to produce a pressurized product gas containing carbon monoxide, hydrogen, carbon dioxide, gaseous sulfur compounds, and particulates. The gasification step is usually carried out at a relatively high pressure of from 20 to 100 atmospheres and a temperature in the range of about 650 C. to 1200 C.
The hot product gas is then cooled to a temperature in the range of about 100 to 250 C., and purified to remove substantially all of the gaseous sulfur compounds and particulate contained therein. The cooled, purified product gas is then passed through a gas enrichment step wherein the hydrogen and carbon monoxide in the product gas are converted to methane and the carbon dioxide removed to produce a high-pressure, synthetic gas consisting essentially of methane and having a heating value of about 33.5 megajoules per cubic meter to about 41 megajoules per cubic meter. In the gas enrichment process, it is often necessary to pass the cooled, purified product gas to a shift reactor prior to methanation to adjust the hydrogen to carbon monoxide ratio in the product gas to a value in the range of about 0.8 to 1 to about 2.5 to 1.
Since these processes depend on relatively high pressures, typically in the range of 20 to 100 atmospheres, the gasifier and all the downstream gas processing equipment, such as the gas cooler, the gas purifiers and the gas enrichment reactors, must be large, thick-walled pressure vessels. Additionally, the connections and cross connections between the various reactor vessels and the gasifier or gasifiers must also be thick-walled pressure containment conduits. Additionally, seals must be provided at each connection point which can withstand the high pressures. These and other complications attendant with high pressure systems significantly increase complexity of the production of synthetic pipeline gas from coal.